The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A pressure vessel is a vessel employed for storing various kinds of fluids such as oxygen, natural gas, nitrogen, hydrogen, etc., and conventionally manufactured by making a nozzle boss and a liner from a metallic material and winding carbon fiber or glass fiber around or stacking on outer sides of the nozzle boss and the liner. In some cases, a conventional pressure vessel manufactured using a metallic liner may be heavy due to the nature of the metal, and may be subject to corrosion, and the manufacturing cost may be relatively high.
Instead of using metal, a plastic liner made of synthetic resin may be manufactured, which may be able to lighten the weight and improve the corrosion resistance compared with the metallic material due to properties of the plastic.
In particular, a Type 4 high-pressure vessel may be manufactured by winding a carbon fiber composite material on a plastic liner in a longitudinal direction and a circumferential direction. A gas such as natural gas or hydrogen gas may be compressed at a high pressure and stored in the high-pressure vessel manufactured as described.
However, if the plastic liner is made of a thermoplastic or thermosetting resin, and the molecular structure of the liner material may be larger than a molecular size of the gas stored in the plastic liner, the gas may escape through a gap between the molecular structures. This phenomenon is referred to as permeation, and the gas escaped through this process is called a permeated gas. Such permeation is distinguished from a leakage in which the gas is leaked due to defects such as a crack between components constituting a connection site or an assembling site or a crack on a material.
As described above, in Type 4 high-pressure vessels, a gas permeation may occur through the plastic liner wall during use. If the permeated gas is trapped in a wall of the composite material and is not properly discharged, pressure between a composite material layer and the liner may be increased, causing the liner to buckle due to the pressure difference between the composite layer and the liner when the gas inside the tank is discharged. In addition, the permeated gas may suddenly be discharged to a periphery of a nozzle or a surface of the tank, which may be mistaken for a leakage and may be recognized as a product defect.